Heat-developable photographic light-sensitive materials and image-formation processes using such materials have heretofore been well known, and are described, for example, in The Fundamentals of Photographic Engineering Corona Co., pp. 553-555, (1979)); Image Information, p. 40, (April, 1978); and Neblette's Handbood of Photography and Reprography, 7th ed., Van Nostrand Reinhold Company, pp. 32-33 (1977).
Typical organic silver salts which are usable in heat-developable photographic light-sensitive materials are silver salts of aliphatic carboxylic acids and those of aromatic carboxylic acids.
In addition, silver salts of aliphatic carboxylic acids having a thioether group, which are described in U.S. Pat. No. 3,330,663, are also usable.
However, these silver carboxylates are defective in that they release acids, after reacting with a reducing agent, to lower the pH value of the photographic film whereby the succeeding development is inhibited.
Other compounds having a mercapto group or a thione group and derivatives thereof are also known as usable organic silver salts.
In addition, silver salts of imino group-containing compounds are known to be usable, such as silver benzotriazoles and derivatives thereof, as described in Japanese Patent Publication Nos. 30270/69 and 18416/70.
However, these silver salts are defective in that they release, after reacting with a reducing agent, compounds that tend to inhibit development, or fog silver halides. Further, these often interfere with the action of spectral-sensitizing dyes to lower the sensitivity of the photographic materials.